Neutral P₄ coordination and reduction at alkaline earth metal centers

The only molecular allotrope of phosphorus, white phosphorus, P₄, is shown to coordinate to main-group metal centers, forming stable complexes, for the first time. Coordinatively unsaturated, Lewis acidic magnesium(II) complexes, Mg(^EtNON^Ar) (^EtNON^Ar; Ar = TCHP, 4,5-bis(2,4,6-tricyclohexylanilido)-2,7-diethyl-9,9-dimethyl-xanthene, or Ar = DCHP, 4,5-bis(2,6-dicyclohexylanilido)-2,7-diethyl-9,9-dimethyl-xanthene) react with P₄ to form 1:1 and 2:1 Lewis adducts, Mg(^EtNON^TCHP)(η²-P₄) and {Mg(^EtNON^DCHP)}₂(μ-η²:η²-P₄), respectively. The related arene-capped complexes of the heavier alkaline earth metals, M(^EtNON^TCHP)(η⁶-toluene) (M = Ca, Sr), also engage in coordination with P₄ to give M(^EtNON^TCHP)(η⁶-toluene)(η¹-P₄). These alkaline earth metal-P₄ complexes appear to reversibly bind P₄ in aliphatic solvents and dissociate P₄ upon dissolution in aromatic solvents. Reduction of P₄ by magnesium(I) complex K₂{Mg( ^{t Bu}NON^Trip)}₂ ( ^{t Bu}NON^Trip = 4,5-bis(2,4,6-triisopropylanilido)-2,7-di(tert-butyl)-9,9-dimethyl-xanthene) and a magnesium(I) synthon K₂{Mg(^EtNON^TCHP)}₂(μ -N₂) provides entry to the planar, aromatic P₄^2– dianion in K₂{Mg(^RNON^Ar)}₂(μ -P₄) (R = tBu, Ar = Trip; R = Et, Ar = TCHP), the hydrolysis of which releases PH₃.